Okay, using the list I posted before...
1. CompassIt doesn't actually do anything; you don't really need it.
2. ParachuteUse to survive a fall into the Spike Pit.
3. Udjat Eye (2.0 only)You don't really need this either. Careful! That fall will kill you if you don't duck into the Spider's Lair.
4. Spike ShoesSteal it from the Yeti's Cave. Use it to stomp the ManTrap.
5. BowFound near the Lava Pit. Use to climb back up to the Spider's Lair. Fire the arrows directly into the walls and use them as climbing spikes. It helps if you alternate walls between shots. You'll need all but one arrow.
6. PistolFound beyond the Octo-Pool. Use it to shoot the Yeti in the Yeti Cave. Make sure you shoot twice!
7. MacheteFound in Yeti Cave. Use to cut down the Rope Pile in the Spider's Lair.
8. PasteFound from defeating the Giant Spider in the Spider's Lair. You'll need your Bombs sticky later.
9. Rope PileFound stuck in a web in a corner of the Spider's Lair. Three Ropes, three places to use them. Use one to get back up to the Spike Pit, another to get back up to the entrance, and the third to get in the Pit of No Return.
10. RockFound in the Spider's Lair. Take it up to the top floor and leave it in the Pitcher's Box on the left.
11. Hedjet (2.0 only)Found in the Pit of No Return. Grab it and run before the exit seals behind you. You don't
need it, but it helps to light things up.
12. BombsFound in the Pit of No Return. Once again, three Bombs, three places you need 'em. Use the first one to get out of the Pit of No Return. Use the second and third to blast the brick walls in the Spike Pit.
13. Sceptre (2.0 only)Found in the Pit of No Return. Place your bomb carefully to free it when you blast your way out. Use it to kill the Shopkeeper in the alcove near the Spike Pit.
14. ShotgunFound near the Spike Pit. In 2.0, the Shopkeeper has it. Use it to blow away Tomb Lord in the Shooting Gallery. It works best to run in, jump, and fire in midair. Tomb Lord only takes one blast.
15. Web CannonFound outside the Crypt. Take it into the Shooting Gallery with you after you deal with Tomb Lord. Use it to build a web bridge across the lava pit inside.
16. Spring ShoesFound in the Shooting Gallery. Use them to jump across the lava pit to the right of the Spike Pit.
17. Pitcher's MittFound to the right of the Spike Pit. Take it to the Pitcher's Box, pick up the Rock you found earlier, stand on the brick block, look up, and throw. You'll hit the Fire Frog and blast down the...
18. MattockFound in the Pitcher's Box. Take it to the bottom floor and break open the Octo-Pool on the left. You can only count on it for one swing, but you can try to use it to cheat, too. I wouldn't recommend it. Use the weapon of your choice to deal with Alien Boss.
19. Climbing GlovesFound in the Octo-Pool. In 2.0, use it in the Pitcher's Box to reach the Key on the top left. In the original, you'll need it to escape the Crypt.
20. Key (2.0 only)Found in the top left corner of the Pitcher's Box. Use it to unlock the Crypt.
21. CapeFound by defeating the Vampire in the Crypt. Use it to drift across the Lava Pit. Kill the Vampire by any means necessary.
22. Kapala (2.0 only)Found in the Crypt. Take it to the back of the Shooting Gallery and collect enough blood from the Yeti King to last a lifetime. You really only need 1 more HP, though.
23. JetpackFound across the Lava Pit. In 2.0, use it to reach the Gold Idol in the Shooting Gallery. In the original, proceed through the roof above the Lava Pit.
24. Gold Idol (2.0 only)Found in the Shooting Gallery. Grab it to open the path above the Lava Pit.
25. Ankh (2.0 only)Found above the Lava Pit. You need at least 2 HP to get it, because there's no way through the barrier emitter otherwise. Once you get it, kill yourself.
26. TeleporterFound above the Lava Pit. In 2.0, you need the Ankh to get it. Once you have it, look up and teleport twice. There's a slight chance of dying from this, but it's only 1/5 for each teleport.
27. SpectaclesCollect your awesome shades and call it a level.